After defibrillation for sudden cardiac arrest defibrillation, many patients remain at risk because their blood pressure and/or pulse is very low or nonexistent post-defibrillation. A low or nonexistent blood pressure and/or pulse with some coordinated ventricular electrical activity is generally referred to as pulseless electrical activity (PEA) or electromechanical dissociation (EMD). When PEA occurs, the prognosis for recovery is very poor and survival rates are low. When left untreated, PEA may be associated with global ischemia and rapidly progressive brain damage. Common courses of treatment include life support measures, such as CPR and the administration of drugs such as epinephrine. However, if cardiac output does not return, PEA is still a significant cause of death post-defibrillation.
U.S. Pat. No. 6,556,865 to Walcott et al. proposes administering a treatment waveform before defibrillation that is insufficient to defibrillate the heart followed by a second treatment waveform that defibrillates the heart and restores organized electrical activity. The first treatment waveform reduces the likelihood of the onset of PEA following the second treatment waveform.
U.S. Pat. No. 6,298,267 to Rosborough et al. proposes an implantable defibrillator that treats PEA after defibrillation by sensing the state of blood flow after defibrillation. If the blood flow is inadequate, the device induces or re-induces ventricular fibrillation and subsequently applies a defibrillation shock to terminate the induced fibrillation.
International Publication No. WO 00/66222 to Rosborough et al. addresses the condition in which cardiac output is not restored after termination of ventricular tachyarrhythmia. Electrical stimulation therapy is applied virtually immediately (i.e., on the order of one minute) after detecting electromechanical disassociation. Once the return of blood flow is detected, the therapy can be stopped.